A typical cable is constructed of metal conductors insulated with a polymeric material. These insulated conductors are generally twisted to form a core and are protected by another polymeric sheath or jacket material. In certain cases, added protection is afforded by inserting a wrap between the core and the sheath. In fiber optics cable, glass fibers are used instead of metal conductors, but a protective sheath is still necessary.
The requirements of these cables is that they exhibit exemplary flame retardancy, high and low temperature resistance, acid and oil resistance, mechanical strength, insulating and jacketing properties, processability, flexibility, and resistance to whitening, and do not emit toxic gases on burning.
A poly(vinyl chloride) resin composition has been used as a flame-retardant material in cable. However, the poly(vinyl chloride) resin composition generates a toxic halogen-containing gas when it burns, and contains heavy metals as stabilizing agents. In addition, poly(vinyl chloride) resin compositions contain plasticizers, which can bleed on the surface of the resin so that the surface of a shaped article obtained from the resin becomes sticky, and the feel of the shaped article becomes inferior. Further, the bleeding can spread to a shaped part adjacent to the shaped article. Bleeding also leads to a deterioration in oil resistance and printing properties.
Thus, it was desired to develop an improved flame retardant resin composition, which was free of the aforementioned problems. To this end, a polyolefin resin composition having aluminum hydroxide or magnesium hydroxide incorporated therein was proposed. It was found, however, that the cost of producing such a composition was rather high, and that the resin had various disadvantages such that, when it was molded into a shaped article, the shaped article expanded, the surface of the shaped article became rough, and the acid resistance of the shaped article became low. Further, in the presence of carbon dioxide and water, the shaped article suffered whitening on its surface due to a magnesium carbonate hydroxide reaction product; the appearance of the shaped article was not acceptable; and the arc resistance and the insulating and mechanical properties were impaired.